A modem converts digital data from a digital device, e.g., an electronic system such as a desktop or laptop computer, or a set-top box for a television, to analog signals for transmission to another digital device. The modem also converts incoming analog signals into digital data for the digital device. A cable modem transmits and receives analog signals over a cable television company's coaxial cable. The cable modem may be an external device or integrated within the digital device.
A cable modem exchanges digital data with a cable modem termination system (CMTS) at the cable television company's office. A CMTS receives data from a cable modem coupled with (or integrated within) a user's customer premise equipment (CPE), e.g., a laptop computer, desktop computer, or television set-top box. The CMTS receives data from the cable modem via a channel in the cable commonly referred to as an upstream channel. The CMTS transmits the received data across a network, e.g., a wide area network, such as the Internet, to a server or another user's CPE, for example. Conversely, when the CMTS receives data from the network, it transmits the data to the cable modem via a channel in the cable commonly referred to as a downstream channel.
There are typically a number of upstream channels between a cable modem and a CMTS. Each cable modem in the cable network is assigned to one upstream channel, which is shared by other cable modems assigned to that upstream channel (by contrast, in a telephone network, each modem is assigned its own separate channel). The downstream channel is shared by all cable modems in the cable network. Thus, data on a downstream channel is identified as intended for a particular cable modem, so that each cable modem can retrieve from the downstream channel the data that is intended for that cable modem.
Data transfer rates on an upstream channel may vary based on, among other things, the number of cable modems using the channel at a particular time. As the number of users increases, there is less available bandwidth for each cable modem on the upstream channel, and thus the data transfer rate decreases. A cable modem is unable to determine when an upstream data transfer rate has decreased, or to improve the data transfer rate. The CMTS may be able to determine that the upstream data transfer rate has decreased, but has limited ability to improve the data transfer rate. The relative inability to improve the upstream data transfer rate may result in a frustrating network experience for a user, whose cable modem is competing with other cable modems for bandwidth to get the user's data to the CMTS as quickly as possible.